1. Field of the Invention
The present invention relates to a method for determining the quantity of fuel leaving an injector of a direct-injection diesel engine and supplying a cylinder of an internal combustion chamber of said engine. The invention relates more particularly to the so-called “common injection rail” engines.
2. Description of the Related Art
In this type of engine, the injection of fuel into the cylinder is conventionally performed in two stages. A first, small quantity of fuel is injected, one or more times, before the top dead center (TDC) point of the piston associated with the cylinder, then a second, greater quantity of fuel after the top dead center point. The injection of said first quantity of fuel, commonly called pilot injection, serves to prepare the combustion of the second quantity of fuel delivered by the following injection, called main injection. The aim of this two-stage injection is notably to reduce the operating noise, the unburned gas emissions and the fuel consumption of the engine.
During the life of the injector, it happens that the quantities of fuel delivered during the pilot injections and the main injections drift from the nominal values supplied by the manufacturer. There are many reasons for these drifts: clogging of the injector, incorrect mounting thereof in the wall of the combustion chamber, wear, etc. These drifts can notably lead to an increase in engine noise and/or in vibrations and/or rattling noises and/or pollutant emissions.
When, following a complaint from the end user, a vehicle has to be analyzed by the constructor network for one of the abovementioned problems, a certain number of inspection points are performed on the vehicle and one of these inspection points consists in checking the correct operation of the injectors.
At the present time, the constructor network has only few means for checking the correct operation of the injectors. The injectors are then generally sent for analysis to the injector manufacturer. In practice, a technician of the constructor network dismantles the injectors and sends them to his component return center which in turn sends them to the injector manufacturer for analysis. The analysis is then carried out in a laboratory with high-technology equipment making it possible notably to accurately measure minute quantities of injected fuel. This transmission and analysis process can take several weeks. For the vehicle not to be immobilized throughout this period, provision is made, after the dismantling of the injectors to be analyzed, for the latter to be replaced with new injectors without waiting for the analysis results. This replacement of the injectors therefore incurs costs which are borne either by the automobile constructor, or by the injector manufacturer, or both, depending on the analysis results.
The analysis results do not, however, always make it possible to determine the exact origin of the problem. In practice, upon its introduction into the analysis laboratory, each injector is generally cleaned, for example by ultrasound, in order to remove the agents (soot, etc.) likely to contaminate the laboratory flow rate measurement appliances used to measure the quantities of fuel leaving the injector. The injector is also sometimes disassembled in order to carry out more comprehensive investigations. The results obtained are therefore the results of analysis of the injector after cleaning and/or disassembly. If the results thus obtained indicate that the flow rate measurement at a predefined reference point is in accordance with a flow rate measurement performed originally at the end of the production line and/or that this measurement remains within a predetermined variation band defined by the constructor, this indicates only that the injector operates correctly after cleaning and/or disassembly. It is impossible to know the exact origin of the problem.
In practice, it is then possible that the injector is not the source of the malfunction, or even that said malfunction has been resolved by the act of cleaning and/or disassembling the injector. This solution is therefore unsatisfactory in terms of costs, diagnosis times and diagnosis made on the basis of the results.
Also, one of the aims of the invention is to propose a non-intrusive method for diagnosing the functionality of an injector by the determination of the quantity of fuel leaving the injector of a direct-injection diesel engine which is simple to implement in the constructor network, which is reliable and which does not require said injector to be dismantled.
The document EP 1 862 659 is known, which notably teaches a method and a device for determining a pilot injection flow rate from the integration, over an angular window of the crankshaft corresponding to the pilot injection, of the instantaneous quantity of heat released in the combustion chamber, obtained from a pressure measurement within the pilot injection band. Such a method requires significant computation and memory means.